Mold clamping and precure of a polymerizable hydrogel

ABSTRACT

An apparatus and method for partially curing a polymerizable monomer or monomer mixture to form a soft contact lens includes a transport device for transporting a plurality of contact lens molds to a precure station in a low oxygen environment, each contact lens mold including a first and second mold half with a polymerizable monomer or monomer mixture therebetween. A clamping member having a plurality of mold engagement members clamps a first contact lens mold half against a second contact lens mold half for a predetermined pressure and time. While the mold halves of the contact lens mold are clamped, the polymerizable monomer or monomer mixture is exposed to a radiant energy source for polymerizing the polymerizable monomer or monomer mixture contained in each contact lens mold.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/825,281, filedMar. 27, 1997, now U.S. Pat. No. 5,981,618, which is a division ofapplication Ser. No. 08/636,507, filed Apr. 26, 1996, now abandoned,which is a continuation-in-part of application Ser. No. 08/257,792,filed Jun. 10, 1994, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an apparatus and method formolding soft contact lenses, and particularly an apparatus and methodfor precuring a polymerizable monomer or monomer mixture under pressureto form a soft contact lens.

2. Discussion of the Prior Art

U.S. Pat. No. 4,495,313 to Larsen, now assigned to the assignee of thepresent application, discloses the polymerization of a monomer to form asoft contact lens by means of ultraviolet light. In addition, thisreference also teaches that an ultraviolet light catalyst can be addedto the polymerization system to effect an essentially completepolymerization.

U.S. Pat. No. 5,039,459 to Kindt-Larsen et al. entitled “Method ofForming Shaped Hydrogel Articles Including Contact Lenses” teaches thepolymerization of soft contact lenses wherein the monomer/diluentmixture in a transparent polystyrene mold is exposed on one side to 1.7jewels/centimeter squared of ultraviolet radiation for ten minutes at55° C. (TL 09 lamps with peak radiation of 350 nm).

In addition to these two references, U.S. Pat. Nos. 4,565,348;4,680,336; 4,640,489 and 5.080,839 all disclose the polymerization of amonomer with ultraviolet light to form a soft contact lens. The entiredisclosure of each of these references are hereby incorporated byreference into this patent application.

SUMMARY OF THE INVENTION

The present invention is an apparatus and a method for precuring apolymerizable monomer mixture to form a soft contact lens in a mold withavoids decentration of the resultant lens, enables a more uniform curefor the lens during the cure step, and which reduces “puddling” orcavitation of the lens in the mold during cure.

In accordance with the present invention, a polymerizable monomer ormonomer mixture is deposited in a lens mold having first concave andsecond convex mold halves. The mold halves are formed of polysytrene orother material transparent to actinic or visible radiation. The moldhalves are transported from the deposition and mold assembly station tothe precure station of the present invention, and clamped together underpredetermined pressure for a predetermined period of time which may bedone in a low oxygen environment. The second or convex mold half may beslightly thinner than the first or concave mold half to enable moldcompliance during cure as the monomer is polymerized. The clampingpressure aligns flanges formed on the first and second mold halves toensure that the flanges are parallel and that the respective curves ofthe molds are aligned. The clamping pressure also seats the secondconvex mold half against an annular edge formed on the first mold halfto essentially sever any excess monomer from the monomer containedwithin the mold.

After a predetermined clamping period, the hydrogel is exposed toactinic or visible radiation, such as an UV light source, to partiallycure the hydrogel to a gel state. After a second predetermined period ofexposure under clamping pressure, the clamping action and the UVradiation may be removed, and the partially precured hydrogel lens istransported in the mold to a curing station for complete polymerizationand cure. Alternatively, a complete cure may be effected in theapparatus.

It is an object of the present invention to provide a novel means forprecuring a polymerizable monomer or monomer mixture to form a softcontact lens. The means includes a transport for intermittentlytransporting a plurality of contact lens molds to the precure station ina low oxygen environment. The contact lens molds include first andsecond mold halves with a polymerizable monomer or monomer mixturetherebetween. The means also include a plurality of means for clampingthe first mold half to the second mold half for a predetermined periodof time in a low oxygen environment. The polymerizable monomer ormonomer mixture is then exposed to actinic radiation for a predeterminedperiod of time while it is under pressure to partially or completelycure the monomer or monomer mixture.

The clamping pressure may be applied by an annular air cylinder, springdriven annular cylinder, or physical weights which allows actinicradiation to pass through the annulus of the cylinder and through one ormore of the mold halves and into the monomer or monomer mixture. Themeans may include a means for controlling the duration and intensity ofthe clamping pressure, and the duration and intensity of the actinicradiation. It has been found that under certain conditions involving apre-cure or partial cure of the monomer, that the surface energyattraction between the clamping means and the mold half may result inpremature separation of one or more sets of mold halves from the carrierpallet when the clamping means is retracted at the end of the pre-curestep.

The exact cause of this phenomena is unknown, but the mold halves andmonomer are very light in weight, and the attraction may involve surfaceenergy, static electricity, or migration of minute amounts of oils fromthe mold halves to the clamping means over time. When the precureapparatus cycles, the attracted set of mold halves is stacked on anotherset in a different pallet, eventually leading to rupture of the moldhalves and contamination of the production equipment with partiallycured monomer. While the incidence of such premature separation is low,the cost of shutting down a line operating in a controlled atmospherefor cleaning is very high, and thus to be avoided.

It is therefore an object of the present invention to minimize thesurface energy attraction between the mold halves and the clampingmeans, and the opportunity for premature separation of the mold halvesfrom the carrier pallet.

It is another object of the present invention to provide a clampingmeans which will provide radially uniform pressure to clamp the moldhalves together.

Another object of the present invention is to provide a novel method ofprecuring a polymerizable monomer or monomer mixture to form a softcontact lens. The method includes a step of depositing a polymerizablemonomer or monomer mixture in a contact lens mold having first concaveand second concave mold halves with the monomer therebetween. The moldhalves are then clamped together with a predetermined pressure and thenexposed to radiation to partially polymerize the monomer to a precuredgel-like state. The clamping pressure is then relieved and the lens isthen cured with additional radiation or a combination of heat andradiation.

In the preferred embodiment the radiation source may be actinic,electron beam or radioactive source, but preferably is an ultravioletlamp which irradiates the monomer at 2-4 mW/cm² for 5-60 seconds, butpreferably 20-40 seconds. Radiation may also be from a high intensity UVsource that is pulsed or cycled.

The clamping step aligns the mold halves, causes excess monomer to beremoved from the mold cavity, and seats a compliant second mold halfagainst a first mold half for the precure step.

It is an object of the present invention to precure a polymerizablemonomer or monomer mixture to a gel-like state wherein polymerizationhas been initiated throughout the monomer, and utilize the shrinkage ofthe monomer and the compliance of the mold halves to seal and hold themold halves together for the remainder of the cure period. Thissubstantially avoids decentration defects which can occur if the backcurve mold half is tipped or rotated with respect to the front curvemold half prior to cure.

It is another object of the present invention to precure the hydrogel ina low oxygen environment to prevent undesired absorption of oxygen bythe monomer.

It is another object of the present invention to provide an adjustablemeans for varying the clamping pressure during the precure step.

It is another object of the present invention to minimize the surfaceenergy attraction between the clamping means and the mold halves whilesimultaneously providing a radially uniform clamping pressure during theclamping step.

It is another object of the present invention to provide a reciprocatingmeans for positioning the actinic light source at an exposure position,and then retracting the light source to a second position for transportof the lens molds.

It is further an object of the present invention to provide an alternatereciprocating means for positioning the lens molds against the lightsource for exposure, and retracting the molds to a second position fortransport.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects and advantages of the present invention forprecuring a polymerizable monomer or monomer mixture may be more readilyunderstood by one skilled in the art with reference to the followingdetailed description of the two preferred embodiments, taken inconjunction with the accompanying figures wherein like elements aredesignated by identical reference numerals throughout the several views.

FIG. 1 is a partially cut away elevation view of one of the embodimentsfor precuring a polymerizable monomer or monomer mixture to form a softcontact lens.

FIG. 2 is an end elevation view of the apparatus illustrated in FIG. 1.

FIG. 3 is a diagrammatic and schematic illustration of one embodiment ofthe invention.

FIG. 4 is a plan view of a carrier used to transport a plurality ofcontact lens molds having a polymerizable monomer or monomer mixturetherebetween to and from the precure station.

FIG. 4(a) is a diagrammatic and cross-sectional view of a pair of moldhalves in the pallet carrier of FIG. 4.

FIG. 5(a) is a diagrammatic illustration of one embodiment of thepresent invention which uses an air driven clamp for clamping the moldhalves together.

FIG. 5(b) is a diagrammatic illustration of a second embodiment of thepresent invention which uses a spring driven clamp for clamping the moldhalves together.

FIG. 5(c) is an elevation view of one of the clamping members used inthe second embodiment illustrated in FIG. 5(b) which illustrates oneclamp construction that minimizes surface energy attraction.

FIG. 5(d) is a top elevation view of the clamping member illustrated inFIG. 5(c).

FIG. 6 is a plan view of a reciprocating portion of the apparatus forprecuring a polymerizable monomer or monomer mixture to form a contactlens.

FIG. 7 is an elevational view of the apparatus illustrated in FIG. 6.

FIG. 8 is an end elevational view of the apparatus illustrated in FIG.6.

FIG. 9 is an elevational end view of a second embodiment of the presentinvention used to precure a polymerizable monomer or monomer mixture toform a soft contact lens.

FIG. 10 is an elevational side view of the apparatus illustrated in FIG.9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is useful in a process for forming soft contactlenses from a polymerizable monomer or monomer mixture. The soft contactlenses are formed in a mold assembly having a first concave and a secondconvex mold half. As illustrate in FIG. 4al, the mold halves are formedof polystyrene transparent to visible and ultraviolet light, with acentral curved section defining a concave surface 31, a convex surface33 and circular circumferential edge 31(c), and integral with said edgean annular essentially uniplanar flange 31(a). At least a part of theconcave surface 31 and the convex surface 33 have the dimensions of thefront or back curves, respectively of a contact lens to be produced inthe mold assembly, and are smooth so that the surface of the contactlens formed by polymerization of said polymerizable composition incontact with the surface is optically acceptable. The mold is thinenough to transmit heat therethrough rapidly and has rigidity sufficientto withstand prying forces applied to separate the mold halves duringdemolding step which occurs after the cure step in the manufacturingprocess.

The present invention is directed to an additional precure stepintroduced between the assembly of the mold with a polymerizable monomeror monomer mixture, and the cure step. The precure step partially curesthe polymerizable monomer or monomer mixture to a viscous gel andinitiates polymerization throughout the mixture. During this precurestep the parallel alignment of the mold halves are “frozen” by theviscous gel like nature of the partially polymerized monomer gel whichprevents decentration and enables unattended and unweighted cure duringthe remainder of the cure period. The addition of this precure step hassubstantially reduced the number of defective lenses resulting fromtraditional methods of manufacture.

The complimentary pair of first 31 and second 33 mold halves whichdefine the shape of the final desired lens are used to direct mold themonomer mixture wherein the mixture is dissolved in a nonaqueous waterdisplacable solvent. After the filling or dosing step, in which thefront concave mold half 31 is substantially filled with a polymerizationmixture 32, the concave front mold half 31 is covered with a base moldhalf 33 under a vacuum to ensure that no air bubbles are trapped betweenthe mold halves. The base mold half is then brought to rest on thecircumferential edge 31(c) of the concave front mold half to ensure thatthe resultant lenses are properly aligned and without distortion.

The first and second mold halves are then clamped together. Thisclamping step may be done following assembly of the mold halves, duringprecure, or both. The clamping step displaces any surplus monomer fromthe mold area and properly aligns the mold halves by alignment of themold flanges. When the clamping step occurs in the precure process, themold halves are clamped under pressure, the monomer or monomer mixtureis then exposed to actinic light, preferably from a UV lamp, while themold halves are clamped. Typically the mold halves are clamped forapproximately 40 seconds with 30 seconds of actinic radiation. At thecompletion of the precure step, the monomer or monomer mixture hasformed a partially polymerized gel, with polymerization initiatedthroughout the mixture.

Following the novel precure step, the monomer/diluent mixture is thencured in a UV oven whereby polymerization of the monomer(s) iscompleted. This irradiation with actinic, visible or ultravioletradiation produces a polymer/diluent mixture in the shape of the finaldesired hydrogel lens. After the polymerization process is completed,the two halves of the mold are separated in a demolding step typicallyleaving the contact lens in the first or front curve mold half, fromwhich it is subsequently removed. The front and base curve mold halvesare used for a single molding and then discarded or disposed of. Afterthe demolding step, the solvent is displaced with water to produce ahydrated lens, which when fully hydrated and buffered, will be of thefinal shape and size which, in most cases, is nominally 10% larger thanthe original molded polymer/diluent article.

The present invention is therefore a novel precure step, and includestwo separate embodiments of an apparatus for performing the same. Theprecure step is inserted in the process immediately after thepolymerizable composition is placed in the front curve mold half, andthe mold halves assembled.

The compositions to which this precure step may be directed includecopolymers based on 2-hydroxyethyl methacrylate (“HEMA”) and one or morecomonomers such as 2-hydroxyethyl acrylate, methyl acrylate, methylmethacrylate, vinyl pyrrolidone, N-vinyl acrylamide, hydroxypropylmethacrylate, isobutyl methacrylate, styrene, ethoxyethyl methacrylate,methoxy triethyleneglycol methacylate, glycidyl methacrylate, diacetoneacrylamide, vinyl acetate, acrylamide, hydroxytrimethylene acrylate,methoxyethyl methacrylate, acrylic acid, methacryl acid, glycerylmethacrylate, and dimethylamino ethyl acrylate.

Preferred polymerizable compositions are disclosed in U.S. Pat. No.4,495,313 to Larsen, U.S. Pat. No. 5,039,459 to Larsen et al. and U.S.Pat. No. 4,680,336 to Larsen et al., the disclosures of which are herebyincorporated herein by reference. Such compositions comprise anhydrousmixtures of a polymerizable hydrophilic hydroxy ester of acrylic acid ormethacrylic acid and a polyhydric alcohol, and a water displaceableester of boric acid and a polyhydroxyl compound having preferably atleast 3 hydroxyl groups. Polymerization of such compositions, followedby displacement of the boric acid ester with water, yields a hydrophiliccontact lens. The mold assembly of the present invention describedherein may be used to make hydrophobic or rigid contact lenses, but themanufacture of hydrophilic lenses is preferred.

The polymerizable compositions preferably contain a small amount of across-linking agent, usually from 0.05 to 2% and most frequently from0.05 to 1.0%, of a diester or triester. Examples of representative crosslinking agents include: ethylene glycol diacrylate, ethylene glycoldimethacrylate, 1,2-butylene dimethacrylate, 1,3-butylenedimethacrylate, 1,4-butylene dimethacrylate, propylene glycoldiacrylate, propylene glycol dimethacrylate, diethylglycoldimethacrylate, dipropylene glycol dimethacrylate, diethylene glycoldiacrylate, dipropylene glycol diacrylate, glycerine trimethacrylate,trimethylol propane triacrylate, trimethylol propane trimethacrylate,and the like. Typical cross-linking agents usually, but not necessarily,have at least two ethylenically unsaturated double bonds.

The polymerizable compositions generally also include a catalyst,usually from about 0.05 to 1% of a free radical catalyst. Typicalexamples of such catalysts include lauroyl peroxide, benzoyl peroxide,isopropyl percarbonate, azobisisobutyronitrile and known redox systemssuch as the ammonium persulfate-sodium metabisulfite combination and thelike. Irradiation by ultraviolet light, electron beam or a radioactivesource may also be employed to catalyze the polymerization reaction,optionally with the addition of a polymerization initiator.Representative initiators include camphorquinone,ethyl-4-(N,N-dimethylamino)benzoate, and4-(2-hydroxyethoxy)phenyl-2-hydroxyl-2-propyl ketone.

Polymerization of the polymerizable composition in the mold assembly ispreferably carried out by exposing the composition to polymerizationinitiating conditions. The preferred technique is to include in thecomposition initiators which work upon expose to ultraviolet or visibleradiation; and exposing the composition to ultraviolet or visibleradiation of an intensity and duration effective to initiatepolymerization and to allow it to proceed. For this reason, the moldhalves are preferably transparent to ultraviolet or visible radiation.After the precure step, the monomer is again exposed to ultraviolet orvisible radiation in a cure step in which the polymerization ispermitted to proceed to completion. The required duration of theremainder of the reaction can readily be ascertained experimentally forany polymerizable composition.

After the polymerizable composition has polymerized, the mold assemblyis disassembled to permit further processing of the polymerized hydrogelinto a contact lens (such processing including e.g. washing andhydrating, and packaging of the lens). Preferably, the flanges of thefront and back curve mold halves are gripped and pulled away from eachother, either in directly opposite directions or through an angle in aprying sort of motion. Advantageously, the back curve is first heatedmoderately to facilitate separation of the polymerized article from theback curve mold half surfaces.

THE PRECURE APPARATUS

FIG. 1 and FIG. 2 represent a side elevation view and an end elevationview, respectively, of an apparatus for practicing the presentinvention. As illustrated in FIGS. 1 and 2, a support frame 11 havinglegs 12 provides support for the device at an elevation of an infeedconveyor 33. As shown in FIG. 3, the precure apparatus receives aplurality of pallets, one of which is illustrated in FIG. 4, having aplurality of contact lens molds therein, from the infeed conveyor 13. Asseen in FIG. 3, the infeed conveyor 13 delivers the pallets 30 and molds31, 33 to a low oxygen environment, which environment is accomplished bypressurizing an enclosure 14 with nitrogen gas. Prior to polymerization,the monomer is susceptible to absorption of oxygen which results indegradation of the resultant lens. The enclosure 14 may be pivoted aboutpivot point 15 by lifting on handle member 16. A gas strut assist device17 will hold the enclosure 14 in an open position for servicing of theapparatus.

As illustrated in FIG. 3, the conveyor 13 delivers pallets 30 containinga plurality of molds 31, 33 to an accumulating section generallyindicated 18 which gathers a plurality of pallets for the precure step.In the embodiment illustrated in FIGS. 1-2 and 6-8, twelve pallets ofthe type illustrated in FIG. 4 are accumulated for a total of 96 moldsin each batch operation. In the embodiment illustrated in FIGS. 9 and 10a total of 12 pallets having 96 contact lens molds thereon are batchedfor each precure operation. Accumulator 18 thus enables the precureapparatus of the present invention to batch process a plurality of moldsfor an extended period of time of 30 to 60 seconds while continuouslyreceiving new pallets from the production line at the rate of 1 every 6to 12 seconds.

The precure assembly 19 is partially visible in the breakaway portion ofFIG. 1, and is further described with respect to FIGS. 6-8. It is raisedand lowered into engagement with pallets containing contact lens moldsby virtue of a pneumatic cylinder 20 which raises and lowers anintermediate support beam 21 and reciprocating shaft members 22 whichare journaled for reciprocating support in member 23 as will behereinafter subsequently described in greater detail. After the precureoperation, the pallets with contact lens molds therein are dischargedthrough a nitrogen ventilation airlock mechanism 24 (illustrated inFIG. 1) for subsequent cure by heat and cycled actinic radiation.

The present invention is particularly adapted to cooperate with aplurality of pallets as illustrated in FIGS. 4 and 4a which have aplurality of cavities for receiving a plurality of contact lens molds.As illustrated in FIG. 4a, the contact lenses of the present inventionare formed by placing an amount of polymerizable composition, generallyon the order of about 60 μl, in the first or concave mold half 31. Thedesired amount depends on the dimensions (i.e., the diameter andthickness) of the desired lens, taking into account the generation ofby-products upon polymerization and exchange water for those by-productsand diluent, if any, following polymerization.

Then a second or convex mold half 33 is placed onto the polymerizablecomposition 32 with the first and second mold halves aligned so thattheir axes of rotation are collinear and the respective flanges 31(a),33(a) are parallel. The mold halves 31 are carried in an annular recess30(a) which receives and supports the annular flange 31(a) of the firstor concave mold half. The pallet 30 also has a plurality of recesses30(b) for receiving the concave portion of the mold. The pallet alsocarries a plurality of oriented recesses 30(c) which receive atriangular tab portion 31(c) of the base mold half to provide apredefined angular position. The second or convex mold half 33 alsoincludes a triangular tab 33(c) which overlies tab 31(c) to provide acollinear axis of rotation with respect to the two mold halves. Thepallet 30 illustrated in FIG. 4 also contains a unique bar code number35 for use in pallet tracking and quality control procedures.

FIG. 3 is a diagrammatic representation of a portion of the apparatusmore fully illustrated in FIGS. 6-9 and FIGS. 9-10 which is particularlysuited to an overview of the present invention. As illustrated in FIG.3, the apparatus includes a conveyor system 13 for transporting aplurality of pallets 30 into and away from the precure station. Batchmode forks 36(a), 36(b) are used to gather and move a plurality ofpallets into the precure apparatus.

The apparatus 19 includes multiple vertical reciprocal movements, afirst one of which is in response to movement from air cylinders 20(a)and reciprocating beam 21(a). As the precure apparatus 19 is lowered inthe direction illustrated by arrow A, a plurality of annular clampingmeans 41 will engage the upper annular flange 33(a) of each of the moldhalves contained within pallets 30. A plurality of annular clampingmeans 40 are mounted on and travel with a reciprocating platform 41 ofthe apparatus, and are resiliently mounted therein for a secondreciprocal movement along the direction of arrow B illustrated in FIG.3.

As illustrated in FIGS. 3 and 5(a)-(d), the clamping means 40 are biasedwithin frame 41 by springs 42 (illustrated diagrammatically) which maybe the air spring 42(a) illustrated in FIG. 5a or a helical spring 42 asillustrated in FIG. 5b. As the apparatus is lowered, the clamping meanswill engage and clamp the first and second mold halves together with theforce determined by the spring means 42. When air springs are used, theforce will be determined by the amount of pressure provided to the aircylinder 42(a). While clamping means 40 have been illustrated as fourmembers in FIG. 3 for illustrative purposes, it is understood that inthe embodiments illustrated in FIGS. 6-8 and the embodiment illustratedin FIGS. 9-10 that there are 96 individual clamping means, with anindividual clamping means for each of the mold halves.

Positioned above the clamping apparatus are a plurality of actinic lightsources 44 which may be UV lamps. The lamps are separated from theclamping area by Pyrex glass 100 which separates the precure apparatusinto two separate heat zones. This enables cooling of the actinic lamps44, while maintaining the clamping zone at an optimal cure temperature.The glass 100 also protects the lamps from monomer emissions whichcollect on the glass 100 rather than the lamps 44. After the clampingmeans has engaged the mold halves to clamp them together, a shuttermechanism 45 is opened by air cylinder 46 to enable the actinic lightsource 44 to initiate polymerization of the polymerizable composition ineach of the mold halves 33. Shutter 45 has a plurality of openings 43defined therein and is reciprocal along the x axis as indicated by arrowC in FIG. 3 in order to open and close the exposure passage ways 47.

The operation of the precure apparatus 19 is set by control circuit 10which controls the duration of the clamping period by the length of timeair cylinder 20(a) is activated to its reciprocal down position. Controlcircuit 10 also controls the amount of radiation received by the moldscontrolling the duration of the exposure period through operation ofshutter 45 and air cylinder 46. The intensity may also be manuallyadjusted by raising or lowering the lamps 44 with respect to molds 31,33. Optionally, the polymerization radiation may be generated remotelyand routed to the clamped mold halves and polymerizable material via afiber optic system, with control system 10 providing control of exposuretime and energy level.

The amount of force applied by clamping means 40 may be varied fromapproximately 0.5 Kgf to 2.0 Kgf/per lens and is applied to keep theflange 33(a) of the second convex mold half parallel to the flange 31(a)of the first concave mold half for the duration of the exposure. Theclamping weight is applied for 10 to 60 seconds, but typically for aperiod of 40 seconds by control means 10. After approximately 0-20seconds of weight, preferably 10 seconds, actinic radiation from UVlamps 44 is applied to the assembled mold and the polymerizable monomer.Typically, the intensity of the UV light source is 2-4 mW/cm², and thisintensity of light is applied for 10 to 50 seconds, but in the preferredembodiment, is applied for 30 seconds.

In the preferred embodiment, the UV lamp source are tubular low pressuremercury vapor fluorescent lamps which emit a long wave ultravioletradiation having a highly concentrated radiation between 320 and 390 nm.In one embodiment, by way of example, the lamps are manufactured byPhilips as model ‘TL’ 29 D 16/09 N having a nominal wattage of 14 wattsand an average radiation of 1.8 watts in the desired spectrum.

The mold halves are first clamped together for a predetermined period oftime, prior to exposure, in order to allow equilibrium to developbetween the monomer and the mold cavity, and to allow any excess monomerto be extruded out of the mold cavity into the space between flanges31(a) and 32(a) where it forms a ring of excess monomer 33(a), which isgenerally referred to as a “HEMA” ring when hydroxyethylmethacrylatemonomer is used. The first or concave mold cavity includes a sharpannular edge 31(c) to cleanly contact the convex portion of mold half 33and thereby separate the contact lens 32 from the HEMA ring 32(a). Thepre-exposure clamping period allows for any excess monomer to migratefrom the mold cavity to the HEMA ring, enables the second mold cavity toseat cleanly on parting edge 31(c), and allows an equilibrium to developbetween the mold halves and the monomer.

Although the mold halves may be held together until the monomer(s) arecompletely cured, in the preferred embodiment actinic radiation on theorder of 2-4 mW/cm² is applied for approximately 30 seconds. Differentintensities and exposure times could be used, including pulsed andcycled high intensity UV on the order of 10 to 150 mW/cm² with exposuretimes running from 5 to 60 seconds. In a pulsed or cycled exposure, theactinic radiation may be cycled on for 3 to 10 seconds and then off for3 to 10 seconds with a total of 1 to 10 cycles of radiation. At the endof the radiation period, the shutter 45 is closed by reciprocating it tothe right as illustrated in FIG. 3 and the weight is removed byenergizing cylinder 20(a) to lift the precure assembly 19 upwardly bymeans of push rods 22(a). As the assembly 19 is lifted, the clampingmeans 40 will be lifted clear of the molds and pallets to enable them tobe transported out of the precure means by means of conveyor 13(a).During the precure time, the temperature in the system may be variedfrom ambient to 50° C.

At the conclusion of the precure process, the monomer has gone throughinitiation and some degree of polymerization. The resultant product isin a gel state with some areas of the product that have the leastthickness, i.e., the edge, having a higher degree of polymerization thanthe body. As the monomer polymerizes it forms a seal along the partingedge 31(c), which together with the inherent shrinkage of the monomerfrom polymerization, forms a secure mold package that may be cured inatmospheric conditions.

The clamping pressure aligns the mold flanges to provide substantiallyparallel alignment of the flanges, and the seal maintains them in aparallel position which results in improved optical characteristics nearthe theoretical maximum of the plastic mold halves. Further, theclamping, and resultant seal from the partial cure results in highlyrepeatable values for centration and an improved “clean” edge at thecircumference of the lens.

FIGS. 5a and 5 b are schematic illustrations of two alternate means forclamping the mold halves together. In FIG. 5a an air spring is used todisplace the clamping means 40 downwardly with respect to the movementof reciprocating platform 41. In the embodiment illustrated in FIG. 5b,a resilient coil spring 42 is used to drive the clamping means 40downwardly with respect to the movement of reciprocating platform 41.The clamping means 40 illustrated in FIGS. 5(c) and 5(d) is particularlyadapted for use with the embodiment illustrated in FIG. 5(b), but withminor modifications could be used in the embodiment of FIG. 5(a).

As illustrated in FIG. 5a, reciprocating platform 41 includes aplurality of annular cylinders 40, each of which has an annular flange51 formed thereon, which reciprocates within a cylinder defined byspacer plate 52 to form an air spring or air cylinder 42(a). Thecylinder is vented to atmosphere by vents, one of which is illustratedat 53 in FIG. 5a to enable air pressure in the air cylinder 42(a) todrive the flange 51 and clamping means 40 downwardly against a stopplate 55 when the air cylinder 42(a) is pressurized. The carriage 50also includes an upper stop member 56 which defines the upper limit oftravel by annular flange 51, and serves as reciprocal bearing supportfor the clamping means 40. The upper stop member 56 also defines aplurality of air plenums, one of which is schematically illustrated at71, which provide air pressure for the air cylinder 42(a).

Air pressure is supplied to plenum 71 by solenoid air valve 72 which isactivated by control means 10. As indicated previously, the air pressuresupplied to air cylinder 42(a) is variable to generate a clamping forceof 0.5 Kgf to 2.0 Kgf on the annular flange 33(a). As the reciprocatingplatform 41 is lowered over the pallet 30 and the contact lens molds,the annular clamping means 40 and the plurality of engagement membersformed thereon engage the annular flange 33(a) formed on the second orconvex mold half to urge it downwardly and clamp it into engagement withmold half 31. The movement of reciprocating platform 41 is defined bythe movement of the entire assembly 19 as driven by air cylinder 20.

As illustrated in FIGS. 5b-d, the annular clamping cylinder 40 alsoincludes a rectangular flange 51 which is engaged by a resilient coilspring 42 and driven downwardly, as illustrated in FIG. 5b, against stopplate 55. The other end of coil spring 42 is mounted within upper stopplate 56(a). Spacer plate 52 and the upper stop plate 56 provide supportand guidance for the vertical reciprocation of clamping members 40.

The clamping member 40, as illustrated in FIGS. 5(c) and (d) is formedof stainless steel, and optionally the mass of the clamping members maybe increased to enable the clamping members to clamp by weight alone,without air or spring assist. However, the combination of the individualreciprocal clamping means 40 and locally driven resilient biasing meansenable precise control of the amount of clamping pressure exerted on theplastic flanges 33(a) of the upper mold regardless of the amount offorce needed to move the mass of the entire precure assembly 19. Formedon the engaging annulus of clamping number 40 are a plurality ofengagement members 40(a)-(d) which minimize the surface area ofengagement between the clamping member and the mold halves. Theseengagement members are integrally formed from the annular cylinder asdownwardly extending square tooth members, by cutting away portions ofthe annular member. In the embodiment illustrated in FIG. 5(b), 5(c) and5(d), the flange member 51 is rectangular, with mounting holes 51(a),(b) which are used to mount the clamping member to coil spring member42. When formed for use with the embodiment illustrated in FIG. 5(a),flange member 51 would be annular, and member 40 would be uniform indiameter through out its length.

The engagement members 40(a)-(d) are approximately 3.5 mm in thickness,and 4 mm in length, which has been found sufficient to ensure evenlydistributed pressure around the knife edge 31(c) (FIG. 4(a) whileminimizing the area of engagement which might otherwise be susceptibleto surface energy attraction or oil migration from the mold halves.While the preferred configuration for the engagement members isillustrated in FIG. 5(c), any configuration of engagement members40(a)-(d) would work, provided the clamping pressure is distributed in aradially uniform manner about the circular knife edge 31(c). Non-uniformdistribution of the clamping pressure may result in tipping of the upperor back curve mold half with respect to the lower or front curve moldhalf

As noted earlier, while the incidence of attraction between the clampingmember 40 and the clamped set of mold halves is very low, and a verysmall fraction of 1%, the cost in down time associated with changingatmospheres, cleaning the contaminated area, recharging the inertatmosphere and restarting the line is very high.

FIGS. 6-8 are top side and end elevation views of one embodiment of theapparatus for performing the present invention. As illustrated in FIGS.6-8, the precure assembly 19 is mounted on reciprocating support shafts22 which are journaled for reciprocating motion within support members23 which are fixably mounted to a frame. Each of the support members 23include upper and lower bearings or journals 23(a), 23(b) to provide forprecision guidance of the reciprocating shafts 22. Shafts 22 are drivenby intermediate support frame 21 which is in turn driven by air cylinder20 as previously described.

The precure assembly 19 is reciprocated vertically with respect to theupper most surface of the conveyor 13 illustrated schematically in FIGS.7 and 8. The precure assembly 19 is supported from an upper supportframe 60 from which various operating components are suspended byintermediate support members at each corner generally illustrated at 61,62 in FIG. 7 an 62, 63 in FIG. 8. These members suspend thereciprocating platform 41, into which the individual clamping means 40are fitted for a secondary reciprocating along the same axis. A separatesubframe 65 is mounted on platform 41 and provides support for theultraviolet lamps 44 and the ballast members 66 which provide the highvoltage for the UV lamps, and the starters 67 which are used to initiatefluorescence. In one embodiment, by way of example, the ballast membersmay be BTP 30C05S, as manufactured by Philips and the starters may bemodel S2, as manufactured by Philips. The intermediate support frame 65may be lifted free from the reciprocating platform 41 by means of aplurality of handles 67 which are mounted via straps 68 to theintermediate support frame 65. Pyrex glass member 100 separates thelamps 44 from the clamping area to protect the lamps from monomeremissions, and to enable the lamps to be cooled, while keeping theprecure zone at a temperature of ambient to 50° C. to facilitatepolymerization. An oxygen detector 69 is also provided to monitor thelow oxygen environment maintained within the protective cabinet 14 andan alarm is initiated if the oxygen content rises to an unacceptablelevel. Shutter 45 is positioned above the reciprocating platform 41between the UV lamps 44 and the clamping means 40 and is reciprocatedbetween its open and closed position by virtue of air cylinder 46.

The embodiment illustrated in FIGS. 6-8 utilizes the air cylinder or airsprings depicted schematically in FIG. 5a with an internal common plenumformed in the reciprocating platform 41 by means of passageways in stopplate 56. Thus, each of the 96 clamping members 40 are reciprocated bytheir respective air cylinders, which are fed from common plenums, oneof which is illustrated in FIG. 5a as plenum 71 formed in the upper stopplate 56.

FIGS. 9 and 10 depict a second preferred embodiment for practicing thepresent invention. As illustrated in FIGS. 6-8, the first preferredembodiment reciprocated the UV lamps and clamping members into and outof engagement with the mold halves and pallets carried by conveyor means13. In the embodiment illustrated in FIGS. 9 and 10, the UV lamps arestationary, and the pallets are lifted from the conveyor into engagementwith the clamping means for the precure period.

The clamping means utilized by the embodiment illustrated in FIGS. 9 and10 utilizes the clamping means previously described with respect to FIG.5b. In this embodiment, a plurality of clamping means 40(a) are mountedabove a roller conveyor illustrated in side view of FIG. 10 by rollers80. A plurality of lifting standards 81 are positioned between groups ofrollers 80 on centers approximate the width of the pallets 30. In FIG.10, a first row of pallets 30 is depicted resting on rollers 80 withadjoining edges of each of the pallets aligned along the top of thelifting standards 81.

The pallets 30 are aligned in position by means of stop means 83 whichis lifted by air cylinder 82 during the loading of the precureapparatus. During loading of the device, the stop means 83 isreciprocated upwardly, and the requisite number of pallets 30 areadvanced into the precure apparatus. When 6 pallets in each row havebeen advanced, a second stop means 84 is lifted by air cylinder 85 todefine a limit on x axis travel as illustrated in FIG. 10. A separateair cylinder 87 is used in cooperation with stop means 83 to align theadjoining edges of the pallets 30 above the centers of the liftingstandards 81. After the pallets have been aligned, the lifting standards81 are reciprocated upwardly by means of intermediate support frame 88and a pair of pneumatic motors 90 and 91.

The pallets are reciprocated upwardly to the position illustrated at30(a) in FIG. 10, in which position they engage the clamping member40(a) as previously described with respect to FIG. 5b. Each of theclamping members 40(a) also include a separate independent and resilientspring 42 for driving clamping member 40(a) and the upper mold halfagainst the lower mold half during the precure period.

After the pallets and mold halves have been raised by air cylinders 90,91, and the first and second mold halves clamped together by means ofclamping means 40(a), a reciprocating shutter 45(a) is shifted asillustrated in FIG. 3 to align a plurality of openings therein with thecentral openings formed in the clamping means 40(a) and thereby enableexposure of the monomer in the mold halves by means of actinic lightsources 44(a). The upper precure assembly 19(a) is fixably supported bymeans of support beams 92 and 93. High voltage ballast means 66(a) andstarter 67(a) also initiate and maintain fluorescence within the UVlight sources 44(a). The reciprocal subassembly of the embodimentillustrated in FIGS. 9 and 10 is mounted on an intermediate supportframe 94 which may be raised and lowered by means of pneumatic cylinder95 to provide for cleaning and servicing of the apparatus, and inparticular, the clearing of the individual clamping means 40. Pyrexglass member 101 protects the lamps 44(a) from monomer emissions, andmay be removed for clearing. Glass member 101 also divides the apparatusinto two temperature zones, enabling cooling of lamps 44(a). Theintermediate support frame 94 is guided and aligned with the exposureassembly 19 a by means of support rods 95, 96 and reciprocal bushingmembers 97, 98.

The clamping period and the amount of exposure to radiation arecontrolled by control means 10 in the manner previously described withrespect to FIGS. 3 and 5.

Following the precure of the monomer in mold halves 31, 33 the pallets30 are reciprocated downwardly to the position illustrated in FIG. 10and advanced by conveyor rollers 80 to a subsequent conveyor (not shown)which transports the pallets to the final cure apparatus.

While the invention has been particularly shown and described withrespect to the preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention, which should be limited only by the scope of theappended claims.

What is claimed is:
 1. A system for partially curing a polymerizablemonomer or monomer mixture to form a soft contact lens, said systemcomprising: a polymerizable monomer or monomer mixture deposited in acontact lens mold having a first and a second half with said monomertherebetween; a plurality of engagement members that clamp said firstmold half into engagement with said second mold half, said engagementmembers engage only one of said mold halves, each of said members engagesaid one of said mold halves with a predetermined pressure such thatdeformation of said one of said mold halves does not occur; and aradiation source that exposes said monomer to radiation to polymerizesaid monomer to a partially cured state.
 2. The system for partiallycuring a polymerizable monomer or monomer mixture as claimed in claim 1wherein said members clamp said first mold half into engagement withsaid second mold half while in a low oxygen environment.
 3. The systemfor partially curing a polymerizable monomer or monomer mixture asclaimed in claim 1 wherein said radiation source emits actinic, electronbeam or radioactive energy.
 4. The system for partially curing saidpolymerizable monomer or monomer mixture as claimed in claim 1 whereinsaid radiation source is an ultraviolet lamp.
 5. The system forpartially curing said polymerizable monomer or monomer mixture asclaimed in claim 4 wherein said monomer is exposed to 2 to 150 mW/cm² ofultraviolet radiation at a wavelength of 320 to 390 nm.
 6. The systemfor partially curing a polymerizable monomer or monomer mixture asclaimed in claim 4 wherein said monomer is exposed to 2.4 mW/cm² ofultraviolet radiation at a wavelength of 350 nm.
 7. The system forpartially curing a polymerizable monomer or monomer mixture as claimedin claim 1, wherein said members engage said one of said mold halves atevenly distributed spaced locations.
 8. A system for curing apolymerizable monomer or monomer mixture to form a contact lens, saidsystem comprising: a polymerizable monomer or monomer mixture depositedin a contact lens mold having first and a second half with said monomertherebetween; a plurality of engagement members that clamp said firstmold half into engagement with said second mold half, said engagementmembers engage only one of said mold halves, each of said members engagesaid one of said mold halves with a predetermined pressure such thatdeformation of said one of said mold halves does not occur; and aradiation source that exposes said monomer to radiation to polymerizesaid monomer.
 9. The system for curing a polymerizable monomer ormonomer mixture as claimed in claim 8, wherein said members engage saidone of said mold halves at evenly distributed spaced locations.
 10. Asystem for curing a polymerizable monomer or monomer mixture to form acontact lens, said system comprising: a polymerizable monomer or monomermixture deposited in a contact lens mold having a first and a secondhalf with said monomer therebetween , each of said mold halves having anannular flange; a plurality of engagement members that clamp said firstmold half into engagement with said second mold half, each of saidmembers engage said first mold half with a predetermined pressure, withsaid annular flanges of said mold halves substantially parallel; a firstradiation source that exposes said monomer to radiation at a firstlocation to polymerize said monomer to a partially cured state to sealsaid mold halves together, in alignment; and a second radiation sourcethat exposes said monomer to radiation in a subsequent cure at a secondlocation different from said first location to polymerize said monomerto a completely cured state; wherein said monomer is enclosed withinsaid sealed mold halves during the exposure resulting in said partiallycured state and said subsequent cure.
 11. A system for curing apolymerizable monomer or monomer mixture to form a contact lens, saidsystem comprising: a polymerizable monomer or monomer mixture depositedin a contact lens mold having a first and a second half with saidmonomer therebetween; a plurality of engagement members that clamp saidfirst mold half into engagement with said second mold half, each of saidmembers engage one of said mold halves with a predetermined pressure; afirst radiation source that exposes said monomer to radiation at a firstlocation to polymerize said monomer to a partially cured state; and asecond radiation source that exposes said monomer to radiation at asecond location different from said first location to polymerize saidmonomer to a completely cured state; wherein said monomer is enclosedwithin said mold halve during the exposure resulting in said partiallycured state and the exposure resulting in said completely cured state.12. The system for curing a polymerizable monomer or monomer mixture asclaimed in claim 11, wherein a low oxygen environment is provided duringthe exposure resulting in said partially cured state, and wherein anatmospheric condition is provided during the exposure resulting in saidcompletely cured state.